1. Field of the Invention
This invention relates generally to the treatment of coke oven or generator gases which result from the distillation of coal. Specifically, this invention relates to the separation of coal tars from coal coking gases.
2. Description of the Prior Art
Two-step separation of tar is known, in principle, in the art as described in Ullmanns Encyclopedia of Industrial Chemistry (Ullmanns Encyclopadie der Technishen Chemie), Vol. 10, pp. 291-292, FIG. 2 (1958). During the performance of the process therein described, wherein gas suction developed from the coke operation is applied to the condensates, a fraction of the thick tar phase is separated from the tar phase, in a pressure separator, in addition to water. The thick tar phase, which is quite viscous and slurry-like, contains a significant amount of solids, especially coal and carbon dust. This fraction of the thick tar phase, mixed with the normal tar phase, is then conveyed into a tar tank where most of the solids contained therein settle out. Because of this settling, the tar tank must be cleaned at relatively short intervals of time. The cleaning is done manually, a process which is highly distasteful to those who must perform it.
To overcome the problem of frequent manual cleaning of the tar tank, an attempted improvement has been made. A colloid mill has been tried between the pressure separator and the tar tank. The colloid mill reduces the size of the solids in the thick tar phase resulting in less frequent cleanings of the tar tank. However, the solids which do not settle out are carried from the tar tank to a tar distillation unit. These solids produce contamination of the distillate and increase the frequency of required cleaning of the tar distillation unit.
There is a need for improving the above described two-step method of tar separation such that the tar which is separated in the pressure separator will not include solids, thus eliminating the need for frequent cleaning of the tar tank or the need for a colloid mill and its attendant problems of contamination of the tar distillation unit.